Investigating the effects of in vitro photodynamic treatment with two metallo-phthalocyanines in MCF-7 breast cancer cells

Abstract:

Established therapies currently in use for the treatment of breast cancer are high risk,
since their employment harbors multiple undesirable and detrimental side effects. In
many cases these are associated with poor therapeutic outcome managing only to
briefly extend patient lifespan. As a result, many newly designed treatments have
surfaced that aim to effectively remove cancerous tissue and improve survival rates
while minimizing the aggressive onsets to the patient. Photodynamic Therapy (PDT)
has, for a long time, been targeted as a combatant for cancer. Its therapeutic
mechanism is based on the tumor-specific intracellular localization of a
photosynthetic compound, i.e: photosensitizer, prior to its irradiation-mediated
excitation thereby generating high levels of reactive oxygen species (ROS). At the
molecular level, this causes irreversible photodamage to vital intracellular targets
resulting in cell death.
The plasma membrane-, mitochondrial-, lysosomal-, and endoplasmic reticulum
systems are all prime targets of PDT and vary in susceptibility depending on both the
type of cancer being treated and the photosensitizer administered. Newly designed
photosensitizers are governed by their enhanced structural properties to localize and
therefore target certain areas of a cell. Since each cancer type has a unique set of
susceptible and resistant characteristics, knowledge of each new photosensitizers’
range, efficiency, and mechanism of cell death is required. This enables pairing of
these drugs to appropriate cancer types for maximal PDT effect.
Here, two newly designed metallo-phthalocyanine photosensitizers, AlPcSmix and
GePcSmix, were analyzed for their photodynamic effect on the estrogen-positive,
breast cancer cell line, MCF-7. Being one of the most reliable cell lines, it is a
prominent research model because it mimics the problems encountered with tumor
resistance to therapy induced cell death via pathway restrictions. Photosensitizer
administration and excitation by light irradiation to this cell culture system was
therefore referred to as in vitro Photodynamic Treatment (in vitro PDT) and not
Therapy.
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Initial dosage and time responsive studies confirmed that 35 μM AlPcSmix and 115
μM GePcSmix both excited using 15 J/cm2 at 680 nm proved most effective in
reducing viability, whilst individually contributing little adverse influence to cellular
homeostasis. Using these dosages, in vitro PDT analysis on several cellular
parameters indicated a complex mode of cell death was induced. Morphology
revealed typical markers consistent with apoptotic, autophagic and necrotic cell death
while variations in proliferation and cytotoxicity levels were inconsistent with stress
responses observed. This correlated with the detection for four common apoptotic
markers which also revealed discrepancies within the death pathway as possible
mutational deficiencies may have rendered MCF-7 cellular systems incomplete.
Taken together, the wide range of cellular parameters studied suggests cells undergo
a mixture of death modes interchanging via a complex system of molecular switches
over time that concludes in secondary necrosis. This was attributed to the assortment
of sulphonated phthalocyanine species enabling a broad intracellular distribution
range coupled with the non-specific targeting action typical of the ROS generated, in
addition to the absence of a phagocytic conclusion to the death process. In vitro PDT
with AlPcSmix was shown to harbor a greater toxicity to GePcSmix as cells
completed the death response within a shorter time period however, both promoted
MCF-7 population cell death sufficient enough to warrant further study for their use as
potential agents in the PDT of breast cancer.